Method of injection die casting

ABSTRACT

A method of injecting molten metal into a die cavity in a pressure die casting operation using a die which removably seats on a nozzle fed from an injection pump having a reciprocable plunger movable to cover entry ports in the pump chamber. After the plunger is advanced to close the ports and fill the die cavity, the plunger is locked and pressure by the plunger is maintained for a predetermined time, after which the pressure is released, followed after a further predetermined time by a short retraction and re-locking of the plunger while the die is being retracted from the nozzle.

United States Patent Graham 1 Oct. 31, 1972 [54] METHOD OF INJECTION DIE1,999,961 v 4/1935 Daesen ..l64/l l9 CASTING 1,618,223 2/1927 Pierce..l64/3l8 3 270,378 9/1966 Madwed ..164/3l8 [72] Inventor: Eric PurdyGraham, Peterborough,

Ontario, Canada 3,474,854 10/1969 Mace ..164/318 [7 3] Assignee: FisherGauge Limited, Peter- Primary Examiner Robert Baldwin omano CanadaAssistant Examiner-Joan S. Brown [22] Filed: Sept. 29, 1970Atwmeywestell & Hanley [21] Appl. No.: 76,558 [57] ABSTRACT I A methodof injecting molten metal into a die cavity [30] Forms" ApplicationPriomy D in a pressure die casting operation using a die which 10, 1969Great Britain 2/69 removably seats on a nozzle fed from an injectionpump having a reciprocable plunger movable to cover U-S. 13, entry portsin the pump chamber After the plunger is [51] Int. Cl. ..B22d 27/10advanced to close the ports and n h i cavity the [58] Field of Search..164/1l3, 120, 136, 306, 312, plunger is locked and pressure by theplunger is main 164/313 318 tained for a predetermined time, after whichthe pressure is released, followed after a further predeter- [56]References C'ted mined time by a short retraction and re-locking of theUNITED STATES PATENTS plunger while the die is being retracted from thenozzle. 1,927,384 9/1933 Bauer ..164/318 2,119,242 5/1938 Flammang..164/119 2 Claims, 1 Drawing Figure PATENTEDHBIQI I972 3 0 378 r lgl1:! {1:1} I -13 'T"P INVENTOR. ERIC F?! GRAHAM time period until themetal in the die cavity has solidified, after which the plunger retractsand the die is then separated from the injection nozzle. An example ofthis operation is shown in US. Pat. No. 3,256,572 issued June 21, 196.6to Fisher Gauge Works Limited, assignee of William F. Fisher.

This known method has several disadvantages,

namely:

a. The plunger, while maintaining pressure, slowly advances causing themolten metal in the injection chamber to creep past the piston and indoing so erodes the piston an shot sleeve very rapidly, greatly reducingthe effective life of the injection unit.

b. The time during which the die is in contact with the nozzle isdirectly proportional to the time period of pressure maintenance andthus the die is being heated excessively while the nozzle is at the sametime being chilled excessively. This requires additional external heatto the nozzle to render it hot enough for the next casting cycle. Theadditional heat causes rapid oxidation of the nozzle resulting in anabbreviated effective life.

c. If the time period of pressure maintenance is shortened at all, theinjection plunger will retract before the metal in the die cavity haschilled. In so doing, a vacuum is created which extracts the stillmolten metal from the die cavity (suck-back") and results in porouscastings being produced.

d. The injection portion of the cycle commences with the injectionplunger fully retracted and the level of the metal in the gooseneck isat the level of the metal in the melting pot, which means that a portionof the gooseneck chamber is filled with air. Also the nozzle, the gateand the die cavity, are each full of air. As a result, when injectioncommences these combined volumes of air must be forced into the diecavity and compressed until injection pressure is reached. Thiscompressed air will then appear as a void in the casting unless directedinto a gate or a vented area.

e. A further disadvantage in this method is caused by the molten metalreceding from the nozzle, causing immediate chilling of the nozzle. Thisis overcome by additional external heat with the associated problemsoutlined in item (b) above. It should also be noted that the injectionchamber of the pump must be allowed to refill before the die isretracted from the nozzle. If the time is too short, the die willretract from the nozzle as the chamber is filling and the inertia ofthis inrushing molten metal will carry the metal up the nozzle and outthetip, resulting in drops of metal remaining on the outside of thenozzle tip. This prevents proper die alignment for the succeeding cycle.Too long a time period causes excessive chilling of the nozzle with thesame results as those in item (b) above. Also the cycle period isextended resulting in production losses.

The present invention overcomes these disadvantages by providing amethod of injecting molten metal into a die cavity using a die whichremovably seats on a nozzle fed from an injection pump having a plungerreciprocable in a chamber, and closable flow means for entry of moltenmetal into the chamber. The method in its broadest aspect comprises thesteps of, in sequence:

a. seating the die on the nozzle;

b. retracting the plunger and opening the flow means to allow moltenmetal to fill the chamber;

c. closing the flow means and advancing the plunger V to inject moltenmetal under pressure through the nozzle into the die cavity;

d. maintaining pressure by the plunger on the molten metal in thechamber for a predetermined time to offset initial maximum shrinkage ofmetal in the die cavity as the metal in the die cavity solidifies;

e. releasing the pressure by the plunger and locking the plunger in itsadvanced position in the chamber as the metal in the die cavitycontinues to solidify; and

f. after a predetermined time, unlocking and retracting the plunger ashort distance and re-locking the plunger, at the same time retractingthe die from the nozzle.

The accompanying drawing shows, in elevation and partly incross-section, an example injection pump for use with the invention.

In the drawings, a pump 10 is mounted on a pot 11 containing moltenmetal 1111. A plunger 12, hydraulically driven by a cylinder-pistonassembly I3, moves in a cylinder 14 which has a chamber 15 connected bya gooseneck passage 16 to an injection nozzle 17. A gate 20, leading toa cavity 22 of a die 21 which is mounted on arms 23 is removablyseatable on nozzle 17. A plurality of apertures or ports 18, allclosable simultaneously by the downward movement of plunger 12, arelocated circumferentially in the wall of cylinder 14 and open fromchamber 15 into the molten metal Ila of pot I].

In the operation of the injection pump, the die first advances to nozzle17 after which plunger 12 is retracted (upwardly in the drawing) whichopens ports 18 and allows chamber 15 to fill with molten metal throughthe ports from pot 11. When chamber 15 has been filled, plunger 12 isadvanced (downwardly in the drawing) to displace molten metal throughgooseneck passage 16 and nozzle 17 into the die cavity. After the diecavity has been filled in this manner, the pressure exerted by plunger12 is maintained for a predetermined time period, after which thepressure is released but plunger 12 remains locked in its advancedposition.

After a short period in this locked, non-pressurized position sufficientto allow the sprue in gate 20 to freeze, the-die is retracted fromnozzle 17 and plunger 12 is retracted a short distance when it is againlocked in position. i

It will be appreciated that when the die locks on nozzle 17 the nozzleis full of molten metal. Retraction of plunger 12 evacuates air from thesprue and die cavities and this reduces the atmospheric pressure in thedie cavity until chamber 15 is filled with molten metal entering throughports 18. Now when the mold cavity is filled with molten metal by theadvancement of plunger 12, a casting of increased density is obtained,due to less entrapped air.

When the die cavity has been filled, injection pressure is maintainedonly long enough to overcome initial (and maximum) shrinkage of themetal in the cavity as it solidifies or freezes. Pressure on plunger 12by cylinder assembly 13 is then released, but plunger 12 is retained inits advanced position by locking, thus eliminating metal creepage pastthe plunger and resultant excess wear of the plunger.

As the die is retracted from nozzle 17 plunger 12 is retracted a shortdistance (upwardly in the drawing). By this step the overflow of moltenmetal from nozzle 17, caused by warming of the molten metal in thenozzle and the expansion of air trapped in gooseneck passage 16 from theprevious cycle, is prevented. Also sinceplunger 12 is not retractedfully until the next cycle-the possibility of suck-back of molten metalfrom the die cavity is eliminated.

in the present method the die spends less time in contact with nozzle17, which minimizes the undesirable l. A method of injecting moltenmetal into a die cavity using a die which removably seats on a nozzlefed from an injection pump having a plunger reciprocable in a chamber,and closable flow means for entry of molten metal into the chamber,comprising the steps of, in sequence:

a. seating the die on the nozzle;

b. retracting the plunger and opening the flow means to allow moltenmetal to fill the chamber;

0. closing the flow means and advancing the plunger to inject moltenmetal under pressure through the nozzle into the die cavity;

d. maintaining pressure by the plunger on the molten metal in thechamber for a predetermined time to offset initial maximum shrinkage ofmetal in the die cavity as the metal in the die cavity solidifies;

e. releasing the pressure by the plunger and locking the plunger in itsadvanced position in the chamber as the metal in the die cavitycontinues to solidify; and

f. after a predetermined time, unlocking and retracting the plunger ashort distance and re-locking the plunger, at the same time retractingthe die from the nozzle.

2. A method as claimed in claim 1 in which a plurality of ports openinginto the chamber and constituting the flow means are opened byretracting the plunger and closed by advancing the plunger.

1. A method of injecting molten metal into a die cavity using a diewhich removably seats on a nozzle fed from an injection pump having aplunger reciprocable in a chamber, and closable flow means for entry ofmolten metal into the chamber, comprising the steps of, in sequence: a.seating the die on the nozzle; b. retracting the plunger and opening theflow means to allow molten metal to fill the chamber; c. closing theflow means and advancing the plunger to inject molten metal underpressure through the nozzle into the die cavity; d. maintaining pressureby the plunger on the molten metal in the chamber for a predeterminedtime to offset initial maximum shrinkage of metal in the die cavity asthe metal in the die cavity solidifies; e. releasing the pressure by theplunger and locking the plunger in its advanced position in the chamberas the metal in the die cavity continues to solidify; and f. after apredetermined time, unlocking and retracting the plunger a shortdistance and re-locking the plunger, at the same time retracting the diefrom the nozzle.
 2. A method as claimed in claim 1 in which a pluralityof ports opening into the chamber and constituting the flow means areopened by retracting the plunger and closed by advancing the plunger.